Can`t take value from html textarea to php variable - php

Question

I made a blogging platform and I have an ajax updated page where I can select which article to display and his comments and add comments. When I leave a comment it takes the logged user info, the article on which the comment has been made but the comment value is not taken to store it in the database. This is the code :
<div align="center">
<h3>Comentarii:</h3>
<form method="POST">
<textarea rows="4" cols="50" name="comentariu" placeholder="Comenteaza">
</textarea><br>
<input type="submit" name="submit"><br>
<hr>
</form>
</div>
<?php
$comnou = $_POST['comentariu'];
$comuser = $_SESSION['user'];
$conadaugacom = mysqli_connect("localhost", "root", "", "blog");
$sqladaugacom = "insert into comentarii (continut_comentarii,
user_comentarii, articol_comentarii) values ('$comnou', '$comuser', '$ta')";
mysqli_query($conadaugacom, $sqladaugacom);
mysqli_close($conadaugacom);
?>
AJAX Code ->
function showUser(str) {
if (str == "") {
document.getElementById("txtHint").innerHTML = "";
return;
} else {
if (window.XMLHttpRequest) {
xmlhttp = new XMLHttpRequest();
} else {
xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
}
xmlhttp.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
document.getElementById("txtHint").innerHTML = this.responseText;
}
};
xmlhttp.open("GET", "getuser.php?q=" + str, true);
xmlhttp.send();
}
}

Answer 1

Make sure that before POST request serialize the data from form.
html
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div align="center">
<h3>Comentarii:</h3>
<form method="POST">
<textarea rows="4" cols="50" name="comentariu" placeholder="Comenteaza">
</textarea><br>
<input type="submit" name="submit"><br>
<hr>
</form>
</div>
Jquery
<script>
$('input').submit(function(e){
e.preventDefault();
var data = $('form').serialize();
$.ajax({
url: 'your_url_to_post.php',
data: data,
success: function(response){
},
type: 'POST'
});
});
</script>
php file
add this line to check comentariu not empty
if(isset($_POST['comentariu'])){
$comentariu = $_POST['comentariu];
}